It amazes me, but there are some inspectors that do not use moisture meters. While what we do is considered a "visual" inspection, the use of moisture meters can be like a seeing-eye-dog for the inspector as he or she otherwise goes "blindly" through the inspection. Many water conditions give themselves away by a variety of means. Sometimes they do not. While I have not yet gotten on board with the use of infra-red cameras, Moisture meters can not only find conditions you can't see, but can also verify conditions that look suspicious. (Someone may be able to convince me someday of the use of infra-red cameras---but for now I just don't think they fit the context of a "Standard Home Inspection"---even though they are very good at assessing these kinds of conditions.)
"False positives" can be a problem with moisture meters--- and knowing the limitations and capabilities of any tool is paramount to the use of that tool. I run my moisture meter all the way around every toilet; around all shower/tub fixtures---including built-in soap dishes and windows in showers/tubs; and, along the floor at tubs/showers. I REALLY don't want to miss the opportunity to find moisture in these areas. With unfinished basements and crawl spaces, these findings can be visually verified or backed up by moisture meter when I am in those areas. Most finish ceiling materials under bathrooms above are not very "forgiving" of leaking fixtures in that bathroom and should be visually checked. Signs of past leaking is common and can be verified as wet or dry by a moisture meter.
One thing that everyone can watch for with vinyl floors is the telltale signs of moisture indicated by a blotchy discoloration that is caused by moisture affecting the back of the vinyl. One can actually "see" the damage through the more translucent surface of the vinyl. This picture is a great example of this kind of discoloration and indicative of considerable moisture under the vinyl---in this case a failed wax seal on the toilet.
PS, for those of you that are new to my blog (or for some other unexplained reason have never noticed) all pictures and smiley-face inserts (emoticons) have messages that show up when you point at them with your cursor.
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WA State, Home Inspector Advisory Licensing Board